Manufacturers of internal combustion engines, particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of nitrogen oxides, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide, particulate matter, and other particulates. In order to reduce the emissions of internal combustion engines, an exhaust gas treatment system is used to reduce particulates from the exhaust gas flowing from the engine.
An exhaust gas treatment system typically includes one or more treatment devices, such as particulate filters, catalytic converters, mixing elements and urea/fuel injectors. The treatment devices are designed to operate at the temperature of the exhaust gas. For example, a treatment device has an operating temperature. The operating temperature is the temperature at which the treatment device effectively and efficiently alters exhaust gas constituents or removes the desired particulates from the exhaust gas.
At times, the exhaust gas temperature may reach too high a point and reach the structural limits of the treatment devices. For instance, the temperature in a particulate filter may be raised to burn off the particulates in the filter to regenerate the filter. However, during this regeneration process, the temperature of the exhaust gas in the filter may reach beyond a point that the filter can sustain its structure. Also, other treatment devices associated with the filter may also reach structural limits from the high heat. Such high temperature condition in which the treatment devices are subject to structural limits is referred to as an over-temperature condition.
When an over-temperature condition is detected in the exhaust system, some vehicles alter their operations in order to prevent temperatures from exceeding the structural limits of the exhaust gas treatment devices. For instance, some vehicles are put in a limp-home mode, in which the vehicles operate in a limited fashion. Therefore, detecting an over-temperature condition accurately (or avoiding false detection of an over-temperature condition) is desirable in order to prevent vehicles from operating in a limited fashion when they do not have to.